How Your Immune System Fights Off a Virus

If Covid-19 has taught us anything, it’s that diet matters.

Maria Cross
Apr 2, 2020 · 8 min read

takes a natural disaster to realize that food does not actually come from shops, that borders are figments of our imaginations, and that everything that we construct to shield ourselves from the natural world is an illusion that can be swept away in seconds by a flood, an earthquake, a wildfire. Or a virus.

The coronavirus crisis is one that we’ve been sleepwalking towards for a very long time. About 11,000 years, in fact. We really should have been better prepared.

In truth, most of us are lucky to be here at all. Once, the survival of our species was determined by natural selection, as it is with all other animals. For virtually the entire history of humanity, beginning with the Palaeolithic era, natural selection meant that our reproductive success was low. The likelihood of a newborn baby growing up to pass on its genes to the next generation was just 30%. Only half of newborns reached the age of 15.

Natural selection is a brutal but effective system, operated throughout the animal and plant kingdoms, that ensures the survival of a strong species at the expense of the weak. However, it no longer applies to humans: we’ve overridden nature.

Today, modern medicine and public health interventions have ‘produced for the first time in human history virtual lack of the operation of natural selection on biological traits of humans.’

That statement was made by Arthur Saniotis and Maciej Henneberg of the Biological Anthropology and Comparative Anatomy Unit of the University of Adelaide, Australia. In their paper, Evolutionary Medicine and Future of Humanity: Will Evolution Have the Final Word? they comment that today, the chance of each individual passing on their genes is around 99%.

No wonder it’s a little crowded on this planet. Everyone survives, not just the fittest.

Which is good, on the one hand, but on the other it means that we are facing a future with a very weakened gene pool. As Sanniotis and Henneberg comment, this does not necessarily spell disaster, as long as technology and medicine can keep up with disease and continue to devise new interventions to correct these weaknesses. Drugs and surgery have kept us ahead of the curve, so far.

How it all began

Since the First Agricultural Revolution 11,000 years ago, and until the middle of the 20th century, infectious diseases were the main cause of death. The revolution spread gradually across the globe and changed the course of history more than any other human phenomenon. It meant that small, settled communities started to grow, and the first states were created. We switched from being hunter-gatherers to being farmers.

Not only did we settle into denser populations, so too did the animals we domesticated, animals that had previously lived only in the wild. Domesticated animals living closely together, and close to us, exposed us to zoonotic diseases — contagious diseases that are able to jump species and infect humans.

This whole new way of living facilitated the spread of ‘crowd infections’. Almost every major infectious epidemic, including smallpox, flu, measles, and mumps, arose after the start of the First Agricultural Revolution, the period that directly followed the Palaeolithic, also known as the Neolithic.

Ever since then, humanity has been plagued with, well, plagues.

With increased urbanisation, and with no idea of how infectious diseases were transmitted, there were initially no public health measures in place to prevent the spread of cholera, typhoid, typhus et al. Lack of public sanitation and basic hygiene, coupled with poor sewage and open cesspits, facilitated the spread of disease.

That all began to change in the nineteenth century, with the introduction of public health sanitation measures. After the introduction of vaccines and antibiotics in the middle of the twentieth century, there was a massive decline in infectious diseases.

In 1969 the US Surgeon General declared that the war against pestilence had been won.

It hadn’t; we were merely lulled into a false sense of security. The last few decades have seen a re-emergence of old pathogens, now resistant to modern drug treatment, and the rise of stronger and more virulent pathogens.

“New parasites (including pathogens) keep emerging and parasites which previously were considered to be ‘under control’ are re-emerging, sometimes in highly virulent forms.” (Mennerat et al 2010)

The problem is that pathogens, including viruses, can evolve and outwit us: they are always one step ahead. We think we are living healthier lives than ever, but in reality, we are only managing our diseases. Up until now we’ve been able to eliminate bacterial infections with antibiotics. Antibiotic resistance is putting paid to that.

A vaccine works by pre-infecting the body with a weakened form of a disease so that it can produce the right antibodies to fight the virus, or bacterium, as it would if infected with the real disease. Not all viral infections can be prevented by a vaccine, so the best we can hope for in those cases is a drug to control the symptoms. An antiviral medicine won’t kill the virus, but it will inhibit its growth.

Then along comes covid-19, and here we all are, up the proverbial creek without a medical intervention or a naturally selected gene pool to paddle with.

The knowledge that most of us would not be here today if natural selection were still in operation is a sobering thought.

But not the end of the matter, because each one of us possesses a potential superpower. Potential, because it requires regular maintenance and safeguarding.

Shout out to your immune system

Coronavirus aside, the one thing standing between you and death, every moment of every day, is your immune system. This work of sublime biochemical engineering, that is always in full-time operation, is vastly undervalued and underappreciated. It’s time to give it the respect it deserves.

A strong immune system won’t stop you from getting the coronavirus, or any other virus, but it may help you fight off infection and recover faster. That is why people who are immunocompromised (those with ‘underlying health conditions’ and the elderly) are considered most at risk.

Bacteria are microscopic in size, but a virus is about a thousand times smaller. Unlike bacteria, a virus needs a host, where they can multiply rapidly: hello humans. They can enter through the mouth, nose, bodily fluids and cuts in the skin.

Let battle commence

Once it comes into contact with a cell in the host’s body, the virus attaches itself to the cell membrane and injects its DNA into the cell. The wall is breeched, and the cell dies. The virus is now able to replicate inside the cell — making as many as 10,000 copies of itself that can then travel to other parts of the body, including the lungs, and repeat the process.

Your immune system responds to an attack from a virus by launching a counterattack. It triggers this attack by first raising your body temperature — creating a fever — to fight infection. A fever may be unpleasant but it a sign that your immune system has responded and is at work.

Part of the prodigious arsenal at the disposal of the immune system are antibodies. Antibodies are proteins made by white blood cells that respond to the attacker, or antigen. The antibody latches on to the virus and disables it. You have millions — billions — of antibodies swimming through your bloodstream all the time, carrying a memory of, and on the lookout for, old diseases they were commissioned to fight in the past.

It can take several days for the immune system to create new antibodies for a new antigen.

There’s no time to idle, so while your body is busy in the lab creating the right antibody for the new virus, other elements of the immune system are launching their own attack to limit the spread of the new virus. These elements include cytotoxic T-cells. This T-cell recognises and kills the cells that have become infected with the virus, preventing the virus from spreading any further.

But the cunning virus has developed means of avoiding detection by a cytotoxic T-cell, by camouflaging the surface of the cell it has invaded.

Your immune system, also pretty smart, knows this, so sends out natural killer (NK) cells that specialise in recognizing and killing these camouflaged cells by injecting them with toxic substances. Both NK and cytotoxic T-cells make these toxins, and proteins called perforin drill holes in the cell membrane and allow the toxin to enter the cell and destroy it.

The infected cell isn’t entirely helpless in this battle: it too puts up a fight by producing proteins called interferons that prevent the virus from replicating. While they do that, they signal to other cells nearby to warn them that there is a virus present, so they too can prepare themselves to fight.

All this while you lie there, seemingly inert, sweating, and bingeing on box sets.

And here’s some really good news. You may or may not have passed natural selection — who knows — but you still have plenty of control over your immune system. Immunity is influenced by external factors, including diet, stress, and environmental chemicals. Just think what smoking and heavy drinking can do.

Diet is a powerful component of immunity. It works at both ends of the spectrum and can be compromised by both under- and over-nutrition.

Undernutrition ‘severely’ reduces the immune systems response, and nowhere is this more stark than in childhood undernutrition in developing countries, where there is a high mortality rate as children succumb to infection. Even mild forms of undernutrition are related to underlying immunodeficiency.

Excessive calorie intake, on the other hand, can lead to inflammation and poor immunity. Obesity means fewer white blood cells to fight infection. It also means more inflammation, which reduces immunity.

“Obesity, like other states of malnutrition, is known to impair the immune function, altering leucocyte counts as well as cell-mediated immune responses.” (Pérez de Heredia et al 2012)

Nothing contributes more to excessive and empty calorie intake than sugar. Sugar negatively impacts the immune system by triggering inflammation and reducing production of phagocytes, white blood cells that are part of the immune system army, and work by ingesting harmful invaders and dead and dying cells.

So what to eat? It has to be a diet that contains the full range of nutrients that contribute to the full armoury of the immune system, from protein to zinc, from vitamin A to selenium. The diet that favoured natural selection throughout our evolution, and saw our ancient ancestors through various ice ages and unimaginable survival challenges — with no medical or public health interventions — and ensured that we, their descendents, got here.

As you might expect, this diet does not include foods that cause excessive weight gain and inflammation, especially processed foods, sugar, refined vegetable oils and refined carbohydrates. Read about that diet here.

A new to-do list

Once we’ve got through this — and even before — your to-do list should also include consideration of other environmental factors that affect immunity, including:

  • Stress management. Read about how you can use diet to strengthen resistance to stress here.
  • Adequate sleep — because “An increasing amount of scientific data indicate that sleep deprivation has detrimental effects on immune function.”
  • Exercise. Exercise helps relieve stress, and also strenghtens immunity by reducing inflammation.

Because even though this too shall pass, it might also be back.


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Maria Cross

Written by

MSc. Registered nutritionist, specialising in diet and mental health. Visit AllYouCanEat.Org.UK for free brain food guide, or to book a consultation


Outstanding stories objectively and diligently selected by 40+ senior editors on ILLUMINATION

Maria Cross

Written by

MSc. Registered nutritionist, specialising in diet and mental health. Visit AllYouCanEat.Org.UK for free brain food guide, or to book a consultation


Outstanding stories objectively and diligently selected by 40+ senior editors on ILLUMINATION

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